Thread cutting device

ABSTRACT

The thread cutting device, for a lockstitch sewing machine, includes an apertured thread puller member having an operating surface for manipulating portions of the needle and bobbin thread with respect to a thread cutter member. The thread cutter member, which extends through the puller member aperture for engagement with an annular groove in the throat plate, includes a knife edge disposed in the aperture in substantially coplanar relationship with the puller member operating surface. During operation of the thread cutting device the puller member simultaneously positions the needle and bobbin threads in advance of the cutter member knife edge which simultaneously severs both thread portions.

United States Patent [191 Killinger [451 July 22, 1975 THREAD CUTTING DEVICE [75] Inventor: Karl H. Killinger, Dover, NJ.

[73] Assignee: The Singer Company, New York,

[22] Filed: Oct. 17, 1974 [21] Appl. No.: 515,807

Primary ExaminrAlfred R. Guest Attorney, Agent, or FirmE. L. Bell; M. J. Breen; R. E. Smith [57] ABSTRACT The thread cutting device, for a lockstitch sewing machine, includes an apertured thread puller member having an operating surface for manipulating portions of the needle and bobbin thread with respect to a thread cutter member. The thread cutter member, which extends through the puller member aperture for engagement with an annular groove in the throat plate, includes a knife edge disposed in the aperture in substantially coplanar relationship with the puller member operating surface. During operation of the thread cutting device the puller member simultaneously positions the needle and bobbin threads in advance of the cutter member knife edge which simultaneously severs both thread portions.

12 Claims, 7 Drawing Figures THREAD CUTTING DEVICE BACKGROUND OF THE INVENTION This invention relates to thread cutting devices for sewing machines and more particularly to a portable thread cutting device for simultaneously severing a bobbin thread strand and one limb of a needle thread loop close to the underside of a throat plate in a lockstitch sewing machine.

A lockstitch is formed in most conventional lockstitch sewing machines by passing a loop of needle thread around a strand of bobbin thread underneath the throat plate to ensnare the bobbin thread on the downward stroke of the needle. The needle thread loop is then drawn up in garrote-like fashion around the bobbin thread below the throat plate on the upward stroke of the needle.

Thread trimming devices adapted to operate beneath the throat plate of a lockstitch sewing machine usually include one or more thread manipulating members to locate the bobbin thread strand and the needle thread loop in predetermined positions with respect to a cutter member. This thread manipulation, which occurs during a primary rotational movement of the thread cutting device as the needle beings to ascend from its downward stroke is followed by a secondary rotational movement of the thread cutting device that severs the needle thread loop and the bobbin thread strand.

In most known thread cutting devices one or more thread manipulating members and one or more thread cutting members occupy a given sector within a generally circular area defined by the radial movement of the thread cutting and thread manipulating members. The usual thread cutting and thread manipulating members also have operating surfaces disposed in different planes along the rotational axis of the thread cutting device below the throat plate. Therefore suitable radial and axial clearances must be provided below the throat plate to accommodate movement of each of these members during the thread cutting operation. However since the space below the throat plate is usually congested with other mechanisms, such as a lockstitch forming loop taker containing the bobbin thread, and the work feed mechanism that operates the feed dog, the clearance space required by the thread cutting device presents interference problems with the other mechanisms disposed below the throat plate.

It is thus desirable to provide a thread cutting device of compact structure having operating surfaces that require minimal radial and axial clearances below a throat plate.

Among the several objects of the present invention may be noted the provision of a novel thread cutting device; a novel thread cutting device wherein a thread manipulating member and a thread cutting member have operating surfaces disposed in substantially the same plane; a novel thread cutting device wherein the thread cutting member extends through an opening in the thread manipulating member; a novel thread cutting device having a thread cutting memberengageable with a groove in the throat plate for preventing thread from passing between the cutter member and the throat plate; and, a novel thread cutting device of compact structure requiring minimal radial and axial clearances below a throat plate.

Other objects and features will be in part apparent and in part pointed out hereinafter.

SUMMARY OF THE INVENTION The present invention relates to a novel thread cutting device for a sewing machine. The thread cutting device, in the preferred embodiment, includes a thread puller member mounted to the underside of a throat plate for rotation about a fixed axis. The puller member includes a flange having an aperture and a leading end portion in the shape of a vertex. The thread cutting device further includes a cutter member mounted to the throat plate for rotation with the puller member about the fixed axis. The cutter member includes a knife edge extending into the aperture of the puller member and a tapered nose portion engageable with an annular groove formed in the underside of the throat plate. During primary movement of the thread cutting device the leading end of the puller member passes through the needle thread loop and across the bobbin thread to position a strand of bobbin thread and a preselected limb of the needle thread loop in front of the cutter blade knife edge. During secondary movement of the thread cutting device the knife edge simultaneously severs the preselected needle thread limb and bobbin thread strand against a fixed ledger blade on the throat plate. Engagement of the cutter blade nose portion with the throat plate groove ensures that the threads being cut do not pass between the cutter blade and the throat plate. After the thread cutting movement is completed the cutter member and puller member undergo reverse rotation to their initial at rest position.

The invention accordingly comprises the constructions hereinafter described, the scope of the invention being indicated in the following claims.

DESCRIPTION OF THE DRAWING In the accompanying drawing:

FIG. 1 is a side elevational view of a portion of a sewing machine incorporating the thread cutting device of the present invention;

FIG. 2 is a plan view of the thread cutting device in an at rest position;

FIG. 3 is a fragmentary sectional view taken on the line 33 of FIG. 2;

FIG. 4 is a plan view showing the thread cutting device as it engages a needle thread loop and a strand of bobbin thread;

FIG. 5 is a view similar to FIG. 4 showing the thread cutting device after it has spread the needle loop and bobbin thread strand prior to severance thereof;

FIG. 6 is an enlarged fragmentary sectional view taken on the line 6-6 of FIG. 5; and

FIG. 7 is a side view taken on the line 77 of FIG. 2

sponding parts throughout the several views of the drawing.

DESCRIPTION OF A PREFERRED EMBODIMENT Referring to the drawing for a detailed description of the present invention a lockstitch sewing machine having conventional stitch forming instrumentalities for producing repetitive stitch tacks such as used in sewing buttons, belt loops, or reinforcing the ends of pocket openings etc. is generally indicated by reference number 10. The sewing machine 10 comprises a work supporting bed 12 which accommodates a throat plate 14. A needle bar 16 endwise reciprocable in a bracket arm Corresponding reference characters indicate corre-- 18 carries a needle 20 that is intermittently received in a needle aperture 22 in the throat plate 14.

A known work clamp 24 for shifting and/or holding fabric on the throat plate 14 is supported on the sewing machine frame (not shown) in the usual manner. A thread cutting device, generally indicated by reference number 26, is mounted to the underside of the throat plate 14 for cooperation with a conventional operating rod 28. Cam devices for shifting the work clamp 24 and effecting operation of the rod 28 are not shown but are of conventional structure and operation.

The thread cutting device 26 comprises a holding member 30 rotatably pivoted to a stud shaft 32. The stud shaft 32 which forms a rotational axis for the thread cutting device 26 is journaled at one end to the underside 34 of the throat plate 14 and journaled at the opposite end to a bracket 35 affixed to the throat plate 34 by a fastener 37. The holding member 30 includes a hub 36 and a gear portion 38 supported on the hub 36, the gear portion 38 being centered on the stud shaft 32. The holding member 30 further includes an arm 40 projecting radially from the hub 36 and terminating in a lip portion 42. An inner locating surface 44 is formed on the arm 40 at the hub 36 and a threaded locating boss 46 is provided on the arm 40 intermediate the lip portion 42 and the inner locating surface 44.

A thread puller member 48 comprises a mounting portion 50 and a flange portion or operating surface 52 offset from the mounting portion at 54. The thread puller member 48 is secured to the arm 40 of the holding member 30 at an opening 56 that embraces the boss 46. Opposite edges 58 and 59 (FIG. 3) of the mounting portion 50 respectively confront the lip portion 42 and the inner locating surface 44 of the arm 40 to position the thread puller member 48 on the holding member 30 at a predetermined orientation. The flange portion 52 of the thread puller member 48, which is spaced from and substantially parallel with the underside 34 of the throat plate 14, includes a leading end portion 60 which is a vertex for a pair of side portions 62 and 64 that generally diverge from the leading end portion 60. The leading end portion 60 and a pair of edges 65 and 67 (FIG. 6) of the side portions 62 and 64, which constitute the periphery of the flange portion 52, are rounded and polished in any suitable known manner. An aperture 66 is formed in the flange portion 52 and extends from the leading end portion 60 to the offset 54 following the general contour of the side portions 62 and 64.

A cutter member 68 comprises a mounting portion 70 and a blade portion 72 offset from the mounting portion 70 at 74. The cutter member 68 is secured to the arm 40 of the holding member 30 against the mounting portion 50 of the thread puller member 48 at an opening 76 that embraces the boss 44. Opposite edges 78 and 80 (FIG. 3) of the mounting portions 70 respectively confront the lip portion 42 and the inner locating surface 44 of the arm 40 to position the cutter member 68 on the holding member 30 at a predetermined orientation. A lock screw 82 threaded in the boss 46 hugs the mounting portions 70 and 50 against the arm 40. Under this arrangement substantially the entire surface of the cutter member blade portion 72 is disposed in the aperture 66 of the thread puller member 48.

A nose portion 84 of the blade 72 extends through the aperture 66 for engagement with an annular groove 86 formed in the underside 34 of the throat plate 14. A knife edge 88 which forms a perpendicular indentation in a side edge 90 of the blade portion 72 has a radial position, with reference to the stud shaft 32, beyond the outer periphery of the groove 86. The knife edge 88 is disposed within the puller member aperture 66 and forms an operating surface that is substantially coplanar with the puller member flange 52 as best seen in FIG. 6.

The throat plate needle aperture 22 has a radial position with reference to the stud shaft 32, at the outer periphery of the groove 86. A ledger blade 94 having a beveled surface 96 terminating in a free cutting edge 98 is secured by a fastener 99 to the underside 34 of the throat plate 14 such that the cutting edge 98 lies at the outer periphery of the annular groove 86 spaced from the needle aperture 22.

In operation of the thread cutting device 26 the operating rod 28 having a rack of gear teeth (not shown) as disclosed in US. Pat. No. 3,783,813 issued Jan. 8, 1974 engages the gear 38 for the usual two phase movement of the holding member 30. During normal operation of the sewing machine 10, when a stitch tack is being formed, the thread cutting device 26 is in the at rest position as shown in FIG. 2. At or near the completion of a stitch tack the operating rod 28 is shifted in a conventional manner such as disclosed in US. Pat. No. 807,676 issued Dec. 19, 1905, to place the puller member 48 and the cutter member 68 in the position shown in FIG. 4. During primary movement of the thread cutting device 26 from the position of FIG. 2 to the position of FIG. 4 the leading end 60 of the thread puller member 48 passes across the needle aperture 22 to' enter a needle thread loop 100 (needle thread source not shown) and spread a strand of bobbin thread 102 from a bobbin thread source 104 carried in a known fashion by a conventional loop taker 106. In this manner the needle thread loop 100 and the bobbin thread strand 102 extend across the side portions 62 and 64 of the flange 52.

During secondary movement of the thread cutting device 26 about the stud shaft 32, the puller member 48 and the cutter member 68 pass from the position shown in FIG. 4 to the position shown in FIG. 5. Since the cutter member nose portion 84 engages the annular groove 86 a needle thread limb 108 and the bobbin thread strand 102 are urged to pass between the nose portion 84 and the puller member flange 52. Consequently the needle thread limb 108 and the bobbin thread strand 102 cannot pass between the nose portion 84 and the throat plate underside 34. The needle thread limb 108 and the bobbin thread strand 102 are thus positioned directly in advance of the knife edge 88 and extend around the rounded polished edge 67 of the side portion 64 (FIG. 6). The needle thread limb 108 merges into and is continuous with a needle thread limb 110 which passes around the rounded polished edge 65 of the side portion 62 and into the needle aperture 22. Since the knife edge 88 is substantially coplanar with the flange 52 the side portion 62 deflectively shields the needle thread limb 110 from severance by the knife edge 88.

Although not shown the secondary movement cycle of the thread cutting device 26 brings the knife edge 88 beyond the position of FIG. 5 to a position wherein the knife edge 88 engages the ledger blade 94 to sever the needle thread limb 108 and the bobbin thread strand 102 in a known manner. The secondary movement cycle also includes the usual reverse shift of the operating rod 28 to place the thread cutting device 26 back into the at rest position of FIG. 2.

Some advantages of the present invention evident from the foregoing description include a puller member operating surface 52 and a cutter member knife surface 88 that are substantially coplanar permitting identical close axial spacing of these surfaces from the underside 34 of the throat plate 14. It will be apparent to those skilled in the art that since the flange or operating surface 52 and the knife edge 88 are coplanar a needle hook 112 of the loop taker 106 can be placed in closer proximity to the throat plate underside 34 than has been previously possible with conventional thread cutting devices. Also, in the present device the coplanar relationship of the flange portion 52 and the knife edge 88 permits a reduction in the conventional depth of penetration of the needle into the needle aperture 22 thereby reducing overall friction between the needle and fabric, and also reducing needle vibration during sewing. The radial clearance required by the thread cutting device 26 in its at rest position and during the primary and secondary movements is minimal due to the compact structural arrangement of the thread puller member 48 and the cutter member 68 on the holding member 30.

In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results obtained.

As various changes can be made in the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawing, shall be interpreted as illustrative and not in a limiting sense.

Having thus set forth the nature of the invention what is claimed herein is:

l. A thread cutting device for simultaneously severing a bobbin thread and one limb of a needle thread loop on a lockstitch sewing machine below a throat plate comprising, a thread puller member mounted on said throat plate for rotation about a fixed axis, said thread puller member comprising a cantilevered flange portion having an aperture, and a blade member mounted on said throat plate for rotatable movement with said puller member about said fixed axis, said blade member having a knife edge disposed in the aperture of said puller member.

2. The thread cutting device as claimed in claim 1 wherein said flange is formed in substantially one plane and said knife edge is substantially coplanar with said flange.

3. The thread cutting device as claimed in claim 2 wherein said throat plate includes an annular groove and said blade member is formed with a nose portion engageable with said annular groove the nose portion of said blade puller member being formed to pass through said aperture for engagement with the annular groove of said throat plate.

4. The thread cutting device as claimed in claim 1 further including a rotatable member supported on said throat plate for rotation about said fixed axis, said thread puller and blade members each including mounting portions for affixation to said rotatatable member for rotation about said fixed axis with the rotatable member, and wherein the cantilevered flange portion of said thread puller member defines a first surface and the knife edge of said blade member defines a second surface, the respective mounting portions of the thread puller and blade members being affixed to said rotatable member such that the first and second surfaces are substantially coplanar.

5. The Thread cutting device as claimed in claim 4 wherein the mounting portion of said thread puller member is disposed between the mounting portion of said blade member and the throat plate.

6. The thread cutting device as claimed in claim 1 wherein the flange of said puller member has a vertex forming a leading end portion of said puller member with side portions extending from said vertex to spread the loop of needle thread and a loop of bobbin thread around the 'side portions of said flange as said puller member rotates in a first direction about said fixed axis.

7. The thread cutting device as claimed in claim 6 wherein said throat plate includes an annular groove and said blade'member is formed with a nose portion engageable with said annular groove, the leading end of the puller member extending beyond the nose portion.

8. The thread cutting device as claimed in claim 7 wherein said nose portion has side portions corresponding to the side portions of said puller member, said knife edge being formed on one of said side portions.

9. The thread cutting device as claimed in claim 8 wherein said knife edge forms a substantially perpendicular indentation of said one of said side portions.

10. The thread cutting device as claimed in claim 9 wherein the fixed axis defines the center of said annular groove, said knife edge being disposed at a greater radial distance from said fixed axis than said annular groove to permit rotatable movement of said knife edge along a path outside said annular groove.

11. The thread cutting device as claimed in claim 1 wherein said throat plate includes an annular groove and said blade member is formed with a nose portion engageable with said annular groove.

12. In a sewing machine having a bed including an apertured work supporting plate, a thread carrying needle endwise reciprocable through an aperture in said work supporting plate, a lockstitch forming loop taker including a thread carrying bobbin arranged in spaced relation beneath said work supporting plate for cooperation with said needle in the formation of stitches, and a device for severing both the needle and bobbin threads beneath said work supporting plate comprising a thread puller member having a thread engaging free extremity movable in a path traversing the path of needle reciprocation in the space between the work supporting plate and the loop taker, the free extremity of said thread puller member being formed with an aperture, and a thread cutting blade member having a free extremity movable in a path traversing the path of needle reciprocation in the space between the work supporting plate and the loop taker, said blade member extremity being formed with a thread cutting knife edge and disposed within the aperture of said thread pulling member so that the free extremity of the blade member does not require any space between the work supporting plate and the loop taker additional to that required for passage of said thread puller member. 

1. A thread cutting device for simultaneously severing a bobbin thread and one limb of a needle thread loop on a lockstitch sewing machine below a throat plate comprising, a thread puller member mounted on said throat plate for rotation about a fixed axis, said thread puller member comprising a cantilevered flange portion having an aperture, and a blade member mounted on said throat plate for rotatable movement with said puller member about said fixed axis, said blade member having a knife edge disposed in the aperture of said puller member.
 2. The thread cutting device as claimed in claim 1 wherein said flange is formed in substantially one plane and said knife edge is substantially coplanar with said flange.
 3. The thread cutting device as claimed in claim 2 wherein said throat plate includes an annular groove and said blade member is formed with a nose portion engageable with said annular groove the nose portion of said blade puller member being formed to pass through said aperture for engagement with the annular groove of said throat plate.
 4. The thread cutting device as claimed in claim 1 further including a rotatable member supported on said throat plate for rotation about said fixed axis, said thread puller and blade members each including mounting portions for affixation to said rotatatable member for rotation about said fixed axis with the rotatable member, and wherein the cantilevered flange portion of said thread puller member defines a first surface and the knife edge of said blade member defines a second surface, the respective mounting portions of the thread puller and blade members being affixed to said rotatable member such that the first and second surfaces are substantially coplanar.
 5. The Thread cutting device as claimed in claim 4 wherein the mounting portion of said thread puller member is disposed between the mounting portion of said blade member and the throat plate.
 6. The thread cutting device as claimed in claim 1 wherein the flange of said puller member has a vertex forming a leading end portion of said puller member with side portions extending from said vertex to spread the loop of needle thread and a loop of bobbin thread around the side portions of said flange as said puller member rotates in a first direction about said fixed axis.
 7. The thread cutting device as claimed in claim 6 wherein said throat plate includes an annular groove and said blade member is formed with a nose portion engageable with said annular groove, the leading end of the puller member extending beyond the nose portion.
 8. The thread cutting device as claimed in claim 7 wherein said nose portion has side portions corresponding to the side portions of said puller member, said knife edge being formed on one of said side portions.
 9. The thread cutting device as claimed in claim 8 wherein said knife edge forms a substantially perpendicular indentation of said one of said side portions.
 10. The thread cutting device as claimed in claim 9 wherein the fixed axis defines the center of said annular groove, said knife edge being disposed at a greater radial distance from said fixed axis than said annular groove to permit rotatable movement of said knife edge along a path outside said annular groove.
 11. The thread cutting device as claimed in claim 1 wherein said throat plate includes an annular groove and said blade member is formed with a nose portion engageable with said annular groove.
 12. In a sewing machine having a bed including an apertured work supporting plate, a thread carrying needle endwise reciprocable through an aperture in said work supporting plate, a lockstitch forming loop taker including a thread carrying bobbin arranged in spaced relation beneath said work supporting plate for cooperation with said needle in the formation of stitches, and a device for severing both the needle and bobbin threads beneath said work supporting plate comprising a thread puller member having a thread engaging free extremity movable in a path traversing the path of needle reciprocation in the space between the work supporting plate and the loop taker, the free extremity of said thread puller member being formed with an aperture, and a thread cutting blade member having a free extremity movable in a path traversing the path of needle reciprocation in the space between the work supporting plate and the loop taker, said blade member extremity being formed with a thread cutting knife edge and disposed within the aperture of said thread pulling member so that the free extremity of the blade member does not require any space between the work supporting plate and the loop taker additional to that required for passage of said thread puller member. 